Refrigeration system with variable speed compressor



REFRIGERATION SYSTEM WITH VARIABLE SPEED COMPRESSOR Filed April 14, 1959K mm mm V mw W V- mm 2 E G H .l v. F B bk 6 8 2 3 5 8 gg a 3 6 2 3 4 4 45 v m P M 7 5 J ATTOQNEY during pull down.

United States Patent 3,010,289 REFRIGERATION SYSTEM WITH VARIABLE SPEEDCOMPRESSOR Henry W. Kuklinski, Mattydale, Salina, N.Y., assignor toCarrier Corporation, Syracuse, N.Y., a corporation of Delaware FiledApr. 14, 1959, Ser. No. 806,288 7 Claims. (Cl. 62-196) This inventionrelates to controlling the temperature of an enclosed space and moreparticularly to a system adapted to condition the air in a cargo spaceof a mobile truck or railway height car.

It is well known in the art that a refrigeration system which is capableof providing both heating and cooling to a refrigerator car is notrequired to operate at full capacity at all times and that some meansfor reducing the capacity of the system is desirable. If, for example,the refrigeration system includes a compressor driven by an internalcombustion engine a significant decrease in wear of the compressor andengine parts may be achieved by operating the engine at low speed whenfull refrigeration capacity is not demanded of the system. In addition,by operating a refrigeration system in this manner a substantial savingin fuel consumption may be effected and substantially lower sound levelsachieved as well as a reduction in the noxious exhaust fumes produced bythe enm'ne which are desirable or necessary features when such a systemis operated within a city or depot. Since the use of an evaporator fanis generally necessary to the eflicient operation of an air conditioningsystem such as might be employed in a railroad refrigeration car, it isdesirable to operate the fan at a low speed when the cooling demand ofthe cargo space is substantially satisfied in order to reduce the powerconsumed and to produce the least amount of dehydration of the cargowhich may include fresh or frozen foods which are generally adverselyaffected by dehumidi-fication. In order to prevent dehumidification ofthe cargo in a refrigerator car, it is further desirable that thetemperature of the evaporator coil be maintained close to the desiredm'r or operating temperature of the area to be conditioned. However,under extreme conditions of temperature and at times when it isnecessary to pull down the temperature of the cargo from the ambienttemperature to the operating temperature, a high cooling capacity andlow evaporator temperature is desirable. At other times it may bedesirable to operate the refrigeration system in a manner to supply heatfrom the coil serving the cargo space in order to maintain the cargo ata desired temperature.

It is also desirable to design a refrigeration system so that it employsstandard components of relatively small size and low initial cost and toemploy an internal combustion engine operating the refrigeration systemwhich is as small as possible and still provides sufficient powerHowever, when using a relatively small engine for this purpose, it isdesirable to provide some type of protection both to prevent high headpressures in the compressor from damaging the components of the systemand to prevent high operating loads from stalling the engine.

Accordingly, it is an object of this invention to provide an improvedrefrigeration system of the type employing an internal combustion enginewherein the speed of the engine, fans and compressor may be decreased inresponse to decreases in cooling demand of the area to be conditioned.

It is a further object of this invention to provide a refrigerationsystem which will tend to maintain a relatively uniform temperature anda high level of humidity in the area to be conditioned.

It is a further object of this invention to provide a 3,010,289 PatentedNov. 28, 1961 refrigeration system having 'means to reduce the speed ofoperation of components of the system under conditions of abnormallyhigh loads or pressures and which may unload the compressor to preventthe engine from stalling.

It is a further object of this invention to provide a refrigerationsystem employing an internal combustion engine of minimal size for therefrigeration capacity required of the system.

It is a further object of this invention to provide a head pressurecontrol in a refrigeration system which is capable of unloading thecompressor and reducing the speed of operation of the engine employed inthe system in response to a predetermined condition of high headpressure.

t is a further object of this invention to provide an improved controlarrangement for a refrigeration system which will operate the system atvarying speeds depending upon the demand made on the system and provideeither heating or cooling when necessary.

These and other objects of my invention which will become apparent byreference to the following description and attached drawings areachieved in the preferred embodiment by providing 'a dual speed internalcombustion engine directly driving the compressor of a refrigerationsystem. The refrigeration system is provided with a hot gas circuit tosupply hot gas to the evaporator coil for heating and so as to removeaccumulated ice if such should exist when the system is not required toproduce refrigeration. A control circuit is provided for therefrigeration system saving a thermostat which controls the throttle ofthe dual speed engine so that as the temperature of the space to beconditioned approaches the desired operating temperature, the dual speedengine is operated at its lower speed and in addition the compressor maybe partially unloaded under these conditions. 'Ihe evaporator andcondenser fans employed in the refrigeration system derive their powerfrom an alternator which is driven by the dual speed engine and the fanspeed is reduced in proportion to the reduction of engine speed byreason of the lower frequency voltage output of the alternator when thesystem is operated at partial capacity. A high head pressure safetycontrol reduces the operating speed and unloads the compressor underconditions of high heads experienced by the cornpressor.

In the drawings:

FIGURE '1 is a schematic diagram of a refrigeration system embodying thepresent invention; and

FIGURE 2 is a schematic diagram of the electrical control circuit of thepresent invention.

Referring to the drawings and more particularly to FIGURE 1, in thepreferred embodiment of my invention I provide a refrigeration systemfor conditioning the cargo space of a railway refrigeration car or truckwhich comprises va reciprocating three cylinder compressor '10discharging into a condenser 11. The condenser 11 discharges liquidrefrigerant through line 12 into receiver 13 having a first compartment14 and a second compartment 15 for the purpose of which will be morefully explained. From receiver 13 liquid refrigerant is conducted toevaporator 22 through liquid line 16 which is interrupted by liquid linesolenoid valve 17 actuated by solenoid 18.

Liquid line 16 has an expansion device 19 therein which may be aconventional expansion valve actuated by a diaphragm 20 and a sensingelement 21 placed at an suction line 25 conducts the refiigerant backinto compressor :10 and the cycle repeated as will be understood bythose skilled in the art.

A dual speed internal combustion diesel engine having first and secondpredetermined operating speeds and a solenoid actuated throttle forselecting the operating speed directly drives compressor 10. Engine 30has a cooling system and fluid line 31 conducts the warmed cooling fluidfrom the engine through reevaporator 24 where it is placed in heatexchange relation with refrigerant in the reevaporator and subsequentlyreturned to the engine cooling system through line 32. Unvaporizedliquid refrigerant from suction line 23 is placed in heat exchangerelation with the cooling system of the engine to assure that all of therefrigerant reaching the compressor through suction line 25 is vaporizedregardless of the mode of operation of the system.

The refrigeration circuit of the instant invention is provided withmeans to defrost accumulated ice which may be formed on the evaporatorcoil 22 under normal operating conditions and to provide heat to thearea to be conditioned when the temperature drops below a predetermineddesired operating temperature. The heating defirost system illustratedin the drawing comprises a hot gas line 26 leading directly from thedischarge of the compressor cylinders into the second compartment 15 ofreceiver 13 then through a hot gas defrost and heating solenoid valve 27actuated by solenoid 28 and from there into evaporator 22 bypassingexpansion device 19. When it is desired to defrost evaporator 22 thesolenoid 18 actuates liquid line valve 17 and interrupts therefrigeration cycle by preventing flow of refrigerant into evaporator22. At the same time solenoid 28 opens hot gas valve 27 which permitshot gaseous refrigerant'discharged by compressor to flow through hot gasline 29 directly into the evaporator coil 22. Refrigerant in compartment14 of receiver 13 is vaporized and floods condenser 11 as explained inPatent No. 2,762,206, issued September 11, 1956 to C. M. Ashley.Initially, the hot gas may be partially condensed in the evaporator andabsorbs heat from the evaporator coil melting ice which may have formedon its surface. The partially condensed refrigerant is then conductedthrough suction line 23 into reevaporator 24 where it is placed in heatexchange relation with the warm cooling fluidof the disel engine and isreevaporated so that it enters compressor 10 through suction line 25 inthe vapor state as also explained in the patent referred to above. 7

Internal combustion enganie 30 directly drives compressor 10 throughshaft 33. Pulley 34 mounted on shaft 33 drives pulley 36 mounted onshaft 37 of alternator 38 by means of belt 35. Alternator .38 producesan alternating three phase output current or voltage which serves thedual function of supplying power for the operation of condenser A.C. fanmotor 40 and evaporator A.C. fan motor 41 and of supplying power tooperate the control circuits of the refrigeration system. Fans 40 and 41are of the alternating current type generally designed for 60 cycleoperation.

Engine 30 is of the internal combustion type and in the embodimentdescribed operates at two predetermined speeds. Throttle solenoid 42adjusts the fuel supply of the engine and determines at which of thetwopredetermined speeds the engine will operate. Pulleys 34 and 36 areso constructed as to drive alternator 38 at a speed to produce a 60cycle A.C. output voltage when engine 30 is operating at the higher ofthe two predetermined speeds. When engine30 is operated at the lower ofits two predetermined speeds alternator 38 will be driven at a lesserspeed and consequently the frequency of its output voltage will bereduced in proportion to the change in engine speed. When the speed ofengine 30 is'reduced, it has been found that the speed of fans 40 and 41will correspondingly decrease due to the decreased frequency of thevoltage or current supplied to them by alternator 38 without adverselyaiiecting the controls;

The control circuit employed with the refrigeration system of theinstant invention is shown schematically in FIGURE 2. Electricalconductors 57 and 58 are connected to two of the three electrical outputconductors 39 of alternator 38 which supplies power for the controlmechanism. Connected bet-ween conductors 57 and 58 are three series legsof the control circuit. The first leg may comprise a first thermostaticswitch having a pair of contacts 50 in series with liquid line solenoid18 previously described. Contacts 50 are shown in FIGURE 2 as beingnormally closed when the first thermostat calls for full cooling of thearea to be conditioned. The thermostat may be located at any convenientplace preferably within the compartment or area to be conditioned.Solenoid 18 cooperates with liquid line valve 17, which it controls, tomaintain the valve open when solenoid 18 is energized and to close valve17 when solenoid 18 is deenergized. It will be appreciated thatalternatively contacts 50 may be normally open if desired when callingfor full refrigeration in which event the solenoid 18 would maintainliquid line valve 17 open when the solenoid was deenergized and closedwhen the solenoid was energized.

The second leg of the control circuit comprises a second set of contacts51 which may be'associated with the first thermostatic switch and in anormally open position for full cooling as can be observed from thediagram. Contacts 50 and 51 actually form a single pole double throwswitch under such circumstances since one contact of each pair is at alltimes connected to conductor 57. The other contact of set 51 isconnected to a parallel circuit comprising in one leg heating solenoid28 which, as has been previously described, controls hot gas valve 27and, in the arrangement shown, maintains valve 27 closed when solenoid28 is deenergized. The other leg of the parallel circuit referred to maycomprise relay solenoid 54 in series, with a first set of contacts 52 ofa high pressure switch which will presently be described.

The third leg of the control circuit may comprise relay contacts 55,actuated by relay solenoid 54, in series with a parallel circuitcomprising throttle controlsolenoid 42 and suction valveunloading'solenoid 43. The parallel circuit formed by solenoids 42 and43 is in series with a second parallel circuit formed by a second set ofcontacts 53 of the high pressure switch referred to above comprising oneleg of the circuit anda set of contacts 56 of a second thermostaticswitch comprising the other leg; It will be appreciated that the firstand second thermostatic switches may be actuated by separate thermostatssuch as bellows 60 and 61 respectively, or may be actuated -by a singlethermostatic element having a plurality of sets of switch contactsadapted to be actuated at different temperatures.

Unloading solenoid 43 serves to actuate the suction valves 62 or two ofthe three cylinders of compressor 10 and to maintain the two suctionvalves of these cylinders in open position when it is energized therebydisabling two of the three cylinders of the compressor and unloading itby reducing the amount of work done by the compressor when the suctionvalves are open. Throttle solenoid 42 in circuit shown will cause engine30 to operate at the higher of its two speeds when the solenoid isdeenergized and will cause the engine to operate at the lower of its twospeeds when it is energized.

The second thermostatic switch, referred to above, having contacts 56 isset to operate, in the circuit shown in the drawing, at a temperature afew degrees above the desired operating temperature of the area to becondiwhich as shown in FIGURE 2 actually comprises a single pole doublethrow switch, is positioned in the refrigeration circuit so actuator 63senses a predetermined ab normally high head pressure in the cylindersof compressor 10. The high head pressure switch will generally be set tooperate at a pressure just below that head pressure which will indicatea load on compressor which may cause malfunctioning of the compressor orrequire so much power from engine 30 as to put it in danger of stalling.

In the circuit diagram shown in FIGURE 2 all contacts are in theposition they will assume when the temperature of the area to beconditioned is sufliciently higher than the desired operating point setby the first thermostat such that the refrigeration system is operatingat full capacity but without abnormally high head pressure in thecompressor. It will be understood that in FIGURE 2 contacts 51, 53 and56 are shown as being in a normally open position and contacts 50, 52and 55 are shown in a normally closed position under those conditions.The particular configuration of open and closed contacts shown in FIGURE2 is selected merely for convenience of illustration and that otherarrmgements of open or closed contacts may be employed to produce thesame results by merely selecting valves in the refrigeration circuitwhich are normally open and closed depending on whether their associatedsolenoids are energized or deenergized as has been previously explainedwith reference to contacts 50 and valve 17 actuated by solenoid 18.

In operation engine 30 is started and assuming that the first thermostatcalls for full cooling, throttle 42 will be set in a position such thatthe engine runs at the higher .Of its two speeds. Liquid line valve 17will be open and hot gas valve 27 will be closed under whichcircumstances refrigerant will be pumped from compressor 10 throughcondenser 11 into receiver 13 and from the receiver through expansionvalve 19, evaporator 22, reevaporator 24 and back into compressor 10causing cooling of the location in which the evaporator is placed. Bothevaporator 22 and evaporator fan 41 will normally be placed in the cargocompartment of a refrigeration car or other vehicle and cause the sameto be pulled down to the desired temperature. When engine 30 is runningat full speed, evaporator fan 41 and condenser fan 40 will operate atfull speed deriving their power from alternator 38 driven by the engine.

When the temperature of the area to be conditioned drops below thedesired operating temperature, the control circuit will cause liquidline valve 17 to be closed and hot gas valve 27 to be opened.Refrigerant is then pumped from compressor 10 through compartment ofreceiver 13 and directly into evaporator 22 through hot gas line 29. Ifconsiderable frost has accumulated on evaporator 22 some of the hot gasfrom compressor 10 upon heating the cold evaporator may be condensed andflow through suction line 23 into reevaporator 24 where it will bereevaporated and passed through suction line 25 back to the compressor.Reference is made to Patent No. 2,762,206, issued September 11, 1956, toC. M. Ashley for a more complete description of similar defrostingsystems and their application in a refrigeration system such as that ofthe instant invention.

The heating and defrosting operation may be continued until the headpressure in the compressor reaches a point where the high head pressurecontrol switch is actuated. Alternatively, a temperature-responsiveswitch may be attached to the evaporator housing to sense a rise intemperature above the melting point of ice which would indicate that theevaporator has been defrosted. In the preferred embodiment, the firstthermostat having contacts 50, 51 will sense a rise in temperature ofthe conditioned area and put the system back on refrigeration at theproper time.

The operation of the control circuit shown in FIGURE 2 will now bedescribed. The switches of the control circuit are shown in FIGURE 2 inthe position that they would assume when the compartment to beconditioned is at a temperature sufi'iciently above the desiredoperating temperature to call for full cooling. Under these conditionsthe contacts 50 of the first thermostat are closed. Liquid line solenoid18 is energized and therefore liquid line valve 17 is open permittingflow of refrigerant through the evaporator through evaporator 22 in anormal refrigeration cycle. Contacts 51 which as has been previouslyexplained may be associated with first thermostat so as to form a singlepole double throw switch are open under conditions calling for fullcooling. Heating solenoid 28 is therefore deenergized and keeps hot gasvalve 27 closed thereby blocking the entrance of hot refrigerant intoevaporator 22. Contacts 52 actuated by the high pressure switch areclosed under circumstances Where the compressor head pressures are notexcessive. Since contacts 51 are open when the first thermostat callsfor cooling, relay 54 is deenergized and contacts 55 associatedtherewith are closed. Where head pressures in the compressor are notexcessive the contacts 53 in the third leg of the control circuit areopen and where temperatures are above the desired operating point of therefrigeration system and the operating point of the second thermostatcontacts 56 of the second thermostat are likewise open. Under thesecircumstances both throttle solenoid 42 and unloading solenoid 43 aredeenergized so the engine is running at full speed and the compressor isfully loaded.

The second thermostat as previously described is set to operate at atemperature a few degrees above the desired operating temperature of thecompartment to be conditioned. For example, if it is desired to maintainthe cargo space of a refrigerator railway car at a temperature of 35 thesecond thermostat may be set to operate at 37. When the cargo spacereaches 37 on pull down contacts 56 of the second thermostat close.Closing contacts 56 actuates both throttle solenoid 42 and unloadingsolenoid 43 in parallel therewith. Energizing of throttle solenoid 42actuates the throttle of engine 30 and causes it to reduce its speed tothe lower of the two predetermined operating speeds. Energizing ofunloading solenoid 43 causes the suction valves of two of the threecylinders in compressor 10 to remain open during their normal operation.This substantially re duces the amount of work which the compressor iscalled upon to perform and effectively reduces the load on engine 30when the engine is operated at low speed and therefore consequentlyreduces the danger that the engine may stall at low speed.

Furthermore, as engine 30 operates at a lower speed the frequency of theoutput current or voltage of alternator 38 is correspondinglyproportionally reduced. The reduction in output voltage frequency ofalternator 38 correspondingly reduces the operating speeds of fan motors40 and 41. The power consumption of an AC. fan motor is proportional tothe cube of its speed and a significant reduction in power requirementsby the fans is thereby achieved. For example, it has been found thatengine 30 may be operated at 1800 r.p.m. on high speed and 1200 rpm. atlow speed. If alternator 38 is driven so as to produce a 60 cycle outputvoltage at the 1800 rpm. speed of engine 30, by dropping the enginespeed to 1200 r.p.m. the output frequency of alternator 38 is reduced to40 cycles and the fan speeds reduced proportionally without affectingthe operation of the controls adversely.

The refrigeration system continues to operate at low speed cooling untilthe temperature of the area to be conditioned is brought down to thedesired operating temperature set by the first thermostat. While therefrigeration system is operating at low speed the temperature ofevaporator coil 22 is very close to the desired operating temperatureand consequently a means of maintaining a high humidity in therefrigerated compartment may be achieved. As is well known in the art,it is generally highly desirable that the cargo space of a refrigeratorcar be maintained at a relatively high humidity in order to properlypreserve foods contained therein. Since evaporator 22 and evaporator fan41 are generally positioned within the refrigeration compartment and thefan operated to cause circulation of the air within the compartment, thereduction of fan speed circulates a minimum ofair in contact with foodin the cargo space and consequently does not cause as muchdehumidification of the food as would be experienced if a higher fanspeed reaches the desired operating point, the first thermostat which isset to operate at that point opens contacts 50 and closes contacts 51.Opening of contacts 50 deenergizes liquid line solenoid 18 whichinterrupts the refrigeration circuit by closing liquid line valve 17. Atthe same time closing contacts 51 energizes heating solenoid 28 which inturn opens hot gas valve 27 admitting hot gas from compressor intoevaporator 22 to defrost the evaporator if such is required and tosupply heat to the conditioned area until the temperature of the area 7exceeds the desired operating temperature.

Closing contacts 51 also energizes relay 54 thereby opening contacts 55.When contacts 55 are opened both unloading solenoid 43 and throttlesolenoid 42 are deenergized. This reloads the compressor by permittingclosure of the suction valves of all cylinders of compressor 10 andcauses the engine 30 to go into high speed operation. It will be seentherefore that the defrosting operation is normally done at high speedwith a fully loaded compressor and is generally accomplished in a shorttime interval. 7

If during the heating or cooling cycle of the refrigeration systemexcessively high head pressures are experienced by compressor 10, thehigh pressure will actuate the high head pressure switch thereby openingcontacts 52 and closing contacts 53. Opening contacts 52 deenergizesrelay 54 which closes contacts 55. Closing contacts 5S enengizesthrottle solenoid 42 and unloading solenoid 43 thereby unloadingcompressor 10 and reducing the speed of engine 30 regardless of theposition of contacts 56, i.e. the second thermostat. It will beappreciated that if high head pressures occur while the refrigerationsystem of the instant invention is operating, either on the heating or,the cooling cycle, above the predetermined maximum safe operating headpressure set by the head pressure control switch, the system willinstantly go into low speed, unloaded operation providing reducedcapacity heating or cooling. This in turn will prevent engine 30 fromstalling and will prevent damage to the components of the refrigerationsystem. After the excessively high head pressure is reduced below thepredetermined pressure, the head pressure switch will again closecontacts 52 and open contacts 53 putting the system back into high speedoperation assuming that the thermostats do not call for low speedoperation.

When the temperature of the area to be conditioned rises on account ofthe hot gas flowing through evaporator 22 to a point above the desiredopera-ting temperature of the area to be conditioned, contacts 50 of thefirst thermostat will close while contacts 51 will open. This places therefrigeration system on low speed cooling again until such time aseither the temperature in the area'to be conditioned rises causingcontacts 56 of the second thermostat to open, which puts therefrigeration system into high speed cooling, or until the temperatureof the area to be conditioned drops causing contacts 50 to open andcontacts 51 to close, putting the system on high speed heating.

It will be noted that in the system described engine 30 is alwaysoperating as is compressor 10 and that the system is always eitherheating or cooling the conditioned area. If, however, it is desired toprovide a dead hand between heating and cooling the same may be achievedby disassociating contacts 51 from the first thermostat and associatingthem with a third thermostat or a third set of switch contacts which areactuated at a temperature slightly below the desired operatingtemperature.

By means of the system described I am enabled to pro vide arefrigeration system suitable for use in a railway refrigeration car orother transportation cooling system which employs standard alternatingcurrent components throughout and which is simple in operation andeffective for the purposes desired. By providing a dual speed dieselengine in the system and a compressor which is unloaded and operated atlow speed under high loads, I am enabled to employ an engine which maybe sized for the anticipated normal cooling load imposed on the system.This results in cost economies because the engine need not be largeenough to supply all of the power that would be required if thecompressor were fully loaded and operating at high speed during severeoperating conditions as might be experienced upon initial pull down ofthe cargo space. Further, low speed operation of the engine enablesquiet and economical operation of the refrigeration system when maximumcooling capacity is not required. The overall power consumption of therefrigeration system on low speed operation is further reduced byoperating the fans at low speed due to the change in alternator voltagefrequency while at the same time I have found that the alternatorvoltage and frequency is sufficient to operate standard electric andthermostatic controls. If, for any reason, the first thermostatic switchshould fail to operate, the engine and compressor are protected by thehigh head pressure switch from damage. In addition, low speed operationis desirable both from the standpoint of control of noxious exhaustfumes and reduction of noise should the refrigeration car he required tostand in a building or at a depot. Likewise, it has previously beennoted that by operating the evaporator fans at reduced speed and theevaporator coil at a temperature close to the desired operatingtemperature of the cargo space a relatively high humidity is maintainedwhich is desirable in the preservation of many foods.

While I have shown and described the preferred form of my invention itwill be appreciated that the same may be otherwise embodied within thescope of the following claims.

I claim 1. In a refrigeration system having a compressor, a variablespeed internal combustion engine adapted to drive the compressor, anevaporator located in heat exchange relation with air being conditioned,a condenser and an expansion device connected to form a refrigerationsystem, said engine having two predetermined speeds of operation, speedcontrol means associated with said engine to control its speed ofoperation, a thermostatically actuated control circuit for sensing thetemperature of an area to be conditioned, said speed control means beingregulated by said thermostatically actuated control circuit, analternator adapted to be dn'ven by said engine at a speedproportional'to the speed of the engine and thereby adapted to providean alternating electrical current output of a frequency proportional tothe speed' of operation of the engine, a fan having an A.C. motorassociated with said refrigeration system, said fan motor beingelectrically connected to and deriving its power from said alternatorthereby having an operating speed proportional to the frequency of theelectrical output of said alternator, so

that the speed of said fan and the capacity of said refrigeration systemare changed in response to changes in the temperature of the area to beregulated.

2. A control circuit for a refrigeration system having a compressordriven by a dual speed internal combustion engine, an evaporator, anexpansion device and a condenser connected to form a refrigerationsystem, comprising a first thermostatic switch having a pair ofcontacts, the thermostatic element of which is adapted to sense thetemperature in an area to be conditioned and to actuate said firstthermostatic switch at the desired operating temperature of said area,the contacts of said first thermostatic switch being in series with arelay solenoid, a high pressure switch adapted to sense abnormally highhead pressures in the compressor of said refrigeration system and to beactuated thereby at a predetermined pressure, said high pressure switchhaving a pair of contacts in series with said first thermostatic switchand said relay solenoid to form a leg of said control circuit,saidcontrol circuit further comprising another leg connected in parallelwith said first described leg and comprising a series connected circuitcomprising a pair of contacts associated with said relay solenoid andconnected in series with solenoid means for reducing the power demand onsaid internal combustion engine connected in series with a pair of setsof parallel connected switch contacts, one of said sets of contactsbeing actuated by said high pressure switch and the other being actuatedby the thermostatic element of a second thermostatic switch adapted tosense the temperature of said area to be conditioned and to be actuatedat a temperature a predetermined few degrees above the desired operatingtemperature of said area, and means to supply electrical current to thejunctions of the two legs of said control circuit connected in parallel.

3. A control circuit for a refrigeration system having a compressor, anevaporator, a condenser, an expansion device and a dual speed internalcombustion engine to drive the compressor wherein said engine has apredetermined high speed and a predetermined low speed operatingcondition, a throttle solenoid and a throttle adapted to be actuated bysaid throttle solenoid to control the Speed of operation of said engine,said control circuit comprising a thermostatic switch in series withsaid throttle solenoid, the thermostatic element of said switch beingadapted to sense the temperature of an area to be conditioned, saidthermostatic switch and said solenoid throttle being adapted to co-actto change the speed of said engine in response to the cooling demand ofthe area to be conditioned, another thermostatic switch the thermostaticelement of which is adapted to sense the temperature of the area to beconditioned, a solenoid valve in said refrigeration system adapted tointerrupt the refrigeration cycle, the solenoid of said valve being inseries with said other thermostatic switch and cooperating therewith tointerrupt the refrigeration cycle when said other thermostatic switch issatisfied, the first named switch being adapted to be actuated at apredetermined temperature above the desired operating temperature andsaid other thermostatic switch being adapted to be actuated at saidoperating temperature, and an unloading solenoid also in series withsaid first named thermostatic switch adapted to unload a cylinder ofsaid compressor when the temperature of the area to be controlled islower than said predetermined temperature above the operatingtemperature.

4. A control circuit for a refrigeration system having a compressor, anevaporator, a condenser, an expansion device and a dual speed internalcombustion engine to drive the compressor wherein said engine has apredetermined high speed and a predetermined low speed operatingcondition, a throttle solenoid and a throttle adapted to be actuated bysaid throttle solenoid to control the speed of operation of said engine,said control circuit comprising a thermostatic switch in series withsaid throttle solenoid, the thermostatic element of said switch beingadapted to sense the temperature of an area to be conditioned, saidthermostatic switch and said solenoid throttle being adapted to co-actto change the speed of said engine in response to the cooling demand ofthe area to be conditioned, another thermostatic switch the thermostaticelement of which is adapted to sense the temperature of the area to beconditioned, a solenoid valve in said re.- friger-ation system adaptedto interrupt the refrigeration cycle, the solenoid of said valve beingin series with said other thermostatic switch and cooperating therewithto interrupt the refrigeration cycle when said other thermostaticsvu'tch is satisfied, the first named switch being adapted to beactuated at a predetermined temperature above the desired operatingtemperature and said other thermostatic switch being adapted to beactuated at said operating temperature, and means to reduce the speed ofsaid engine to the lower of the two predetermined speeds when the engineis operating at the higher of said predetermined speeds, comprising acompressor head pressure responsive switch associated with saidcompressor and adapted to actuate said throttle solenoid at apredetermined maximum head pressure in said compressor to reduce thecompressor speed and thereby prevent stalling of said engine.

5. In combination: a refrigeration system comprising a compressor havinga plurality of cylinders, a condenser, an expansion device, and anevaporator connected to form a refrigeration circuit; an engineoperatively connected to drive said compressor, said engine having atleast a first operating speed and a second operating speed, said firstoperating speed being greater than said second operating speed, andspeed control means associated with said engine to reduce the speedthereof from said first operating speed to said second operating speed;refriger ant pressure sensing means to sense a refrigerant pressurecondition of said refrigeration system which is indicative of a heavyload being imposed on said engine; compressor unloading means forunloading a cylinder of said compressor; and means to actuate said speedcontrol means to reduce said engine speed from said first operatingspeed to said second operating speed and said compressor unloading meansfrom a loaded condition to an unloaded condition of said compressor inresponse to said refrigerant pressure condition being sensed by saidsensing means to thereby reduce the power demand on said engine whensaid sensing means senses a refrigerant pressure condition indicative ofa heavy load being imposed on the engine.

6. In combination: a refrigeration system comprising a compressor havinga plurality of cylinders, a condenser, an expansion device, and anevaporator connected to form a refrigeration circuit; an engineoperatively connected to drive said compressor, said engine having atleast a first operating speed and a second operating speed, said firstoperating speed being greater than said second operating speed, andspeed control means associated with said engine to reduce the speedthereof from said first operating speed to said second operating speed;a fan associated with said refrigeration system, an alternating currentfan motor connected to drive said fan, and an alternator driven by saidengine at a speed proportional to the speed of said engine andelectrically connected to said fan motor to supply current thereto of afrequency proportional to the speed of said engine so as to drive saidfan at a speed proportional to the speed of said engine; refrigerantpressure sensing means to sense a refrigerant pressure condition of saidrefrigeration system which is indicative of a heavy load being imposedon said engine; compressor unloading means for unloading a cylinder ofsaid compressor; and means to actuate said speed control means to reducesaid engine speed from said first op erating speed to said secondoperating speed and said compressor unloading means from a loadedcondition to an unloaded condition of said compressor in response tosaid refrigerant pressure condition being sensed by said sensing meansto thereby reduce the power demand on said engine when said sensingmeans senses a refrigerant pressure condition indicative of a heavy loadbeing imposed on the engine, said reduction in engine speed also servingto reduce the speed of said fan and fan motor thereby further reducingthe power demand on said engine.

7. In a refrigeration system, a compressor, a dual speed internalcombustion engine adapted to drive said compressor, said engine havingfirst and second predetermined operating speeds, said first speed beinghigher than said second speed, pressure sensing means to sense apredetermined pressure condition in said refrigeration system, anevaporator, a condenser, and an expansion device connected with thecompressor to form a refrigeration circuit, a fan having an AC. motorassociated with said refrigeration system said AC. motor being adaptedto drive said fan at a speed proportional to the frequency of thecurrent supplied to it, an alternator adapted to be driven by saidengine at a speed proportional to the speed of said engine, saidalternator providing an alternating current electrical output having afrequency proportional to the driving speed thereof, said fan motorbeing electrically connected to and adapted to be driven by theelectrical output of said alternator, said pressure sensing means 12being operatively associated with said engine to reduce its speed fromthe predetermined first operating speed to the predetermined secondoperating speed to thereby reduce the speed of said compressor uponsensing said pressure condition, said system serving to reduce the loadimposed on said engine by said alternator when the engine is operatingat the reduced speed condition by reducing the speed of said fan motorproportionally to the reduction in speed of said engine.

References Cited in the file of this patent UNITED STATES PATENTS2,134,107 Dempsey Oct. 25, 1938 2,286,316 Snook June 16, 1942 2,400,665Thomas May 21, 1946 2,462,514 Lehane et al. Feb. 22, 1949 2,498,861Newton Feb. 28, 1950 2,734,346 Dickieson Feb. 14, 1956 2,786,334 WolfMar. 26, 1957 2,887,853 Talmey May 26, 1959 UNITED STATES PATENT. OFFICECERTIFICATE OF CORRECTION Patent No,\ 3,01%289 November 28 1961 Henry WeKuklinski It is hereby certified that. error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 2 line 30,, for "saving" read having} column 3, line 45 for-"enganie" read engine =-q Signed and sealed this 17th day of April1962o (SEAL) Attestz' ESTON G. JOHNSON DAVID L. LADD' Attesting OfficerCommissioner of Patents

